It has been well-known to those skilled in the art to produce carbon paper or carbon sheet by molding carbonaceous fibers in the form of sheets. The carbon paper or carbon sheet obtained by this method, however, suffer from the disadvantage that the individual fibers are bonded to one another with insufficient strength and therefore, the carbon paper or carbon sheet possess unsatisfactory mechanical strength and electrical and other physical properties. To overcome these defects several methods have been developed including, for example, the gaseous-phase thermal-decomposition carbon deposition method and the polymer coating method. The former method involves complicated steps and therefore, the products are inevitably costly. In the products of the latter method, the individual carbon fibers and the polymer are not bonded to each other with satisfactory high strength. In addition, the products of both methods are not completely satisfactory because the voids formed therein are dimensionally nonuniform.
Under the above circumstances, there exists a need for carbon paper or carbon sheet having dimensionally uniform voids and excellent mechanical strength and electrical properties.